Aromatic alkoxyalkanols are useful as industrial surfactants and the corresponding aromatic alkoxyalkanoic acids may be useful as anionic detergents. The aromatic alkoxyalkanoic acids can be prepared in a two-step process by first reacting an aromatic alkanol with ethylene oxide and a suitable alkoxylation catalyst and thereafter converting the aromatic alkoxyalkanol to an alkoxyalkanolic acid.
Japanese Patent No. 50-96516, issued Jul. 31, 1975, discloses a process for the preparation of carboxylic acid salts by the liquid phase dehydrogenation of alcohols with caustic alkali in the presence of precious metal catalysts, including palladium. This process uses a relatively high temperature, 100.degree. C.-270.degree. C. These high temperatures can degrade the ether linkages especially in the highly ethoxylated alcohols.
It is known to use nitroxyl radicals/oxoammonium salts in the oxidation of primary alcohols to produce aldehydes and acids and alcohols to ketones. Journal of Organic Chemistry, vol. 52 (12), pp. 2559-2562: Pure and Applied Chemistry, vol. 62(2), 1990, pp. 217-222; Journal of Organic Chemistry, vol. 55, 1990, pp. 462-466. The primary products produced in these processes are aldehydes and the stoichiometrically consumed oxidant is hypochlorite.
It is generally more difficult to oxidize aromatic alkoxyalkanols than alkanols or primary alkoxyalkanols as it is difficult to oxidize aromatic alkoxyalkanols without splitting the molecular chain at the phenolic ether linkage and thereby producing a large proportion of undesired byproducts or having the aromatic ring undergo oxidation.
It would therefore be advantageous to produce aromatic alkoxyalkanoic acids in high yields and with high selectivities from aromatic alkoxyalkanols without producing large amounts of other products such as alkyl phenols, quinones, polyethylene glycols and oxidized polyethylene glycols.
It has been found that aromatic alkoxyalkanoic acids can be produced in high yields and with high selectivities without the formation of highly corrosive, difficult to separate, side-products by using catalytic amounts of a stable free radical nitroxide, a NO.sub.x -generating compound and an oxidant.